Oscillator system



June 24, 1941. REID 2,246,696

OSCILLATOR SYSTEM Original Filed Aug. 31, 1935 2 Sheets-Shet l ushiyh l63% Home on. GUN 4 Sm w w mum HBM f w w hum 7 mum m l .EWQN 6 W M x AQQNN EN mum W4 93 u .W QHN m %Wv m an INVEN'I'OR John D. Reid PatentedJune 24, 1941 osomLA'ron SYSTEM John D. Reid, Philadelphia, Pa assignorto Radio Corporation of America, a corporation of Delaware,

Original application August 31, 1935, Serial No. 38,762,, now Patent No.2,149,231, dated February 28, 1939. Divided and this application,

tion January 31, 1939, Serial No. 253,829

21 Claims. (01. 250-36) The present invention relates to an oscillatorsystem and more particularly to a variably tuned oscillator for asuperheterodyne radio receiver operating over several differentfrequency bands or ranges including an ultra high frequency range.

This application is a divisional of my application Serial No. 38,762,filed August 31, 1935, now Ratent No. 2,149,231, issued February 28,1939, the invention being directed to the oscillator.

An object of the invention is to provide a stable oscillator tunablenverany of several frequency ranges, particularly an ultra highfrequency range, and characterized by substantial uniformity orsufliciency ofsignal strength or gain throughout any of said ranges.

More particularly, it is an object of my invention to provide a highlystable oscillator, tunable throughout a -wide ultra high frequency rangewith uniform or adequate signal output throughout said range. y

In accordance with the invention, the principal object is attained byproviding a variably is caused to be connected for differing modes ofoperation in a Hartley type of circuit generally and modificationsthereof, depending upon the wave band or frequency range to be covered.Coupling with a mixer tube of improved electrode arrangement is providedbetween cathode and ground of the oscillator.

The invention will, however, be better understood irom the followingdescription when taken in connection with the accompanying drawings andits scope will be pointed out in the appended claims. j

In the drawings,

Fig. 1 is a schematic circuit diagram of a por-- tion of the signalinput circuits of a superheterodyne receiver, including a frequencychanger system embodying the invention, and- Figs. 2, 3 and 4 aresimplified schematic. circuit diagrams of the oscillator portion of thecircuit of Fig. 1, showing connections for three differing modes ofoperation as provided by the circuit of Fig. 1.

tuned oscillator with a plurality of feedback paths from differentanodal electrodes, one of which is a screen grid or additionalelectrode, the feedback path from the anode feeding back principally thelower frequencies 01'. the tunable working range in complementaryrelation to the screen grid feedback path which is deficient in outputsignal strength at the lower end of the range, thereby reinforcing thelower end and giving adequate or substantially uniform gain throughoutthe range.

It is a further object of the present invention to provide an improvedfrequency band or tuning range changing systemfor an oscillator for asuperheterodyne receiver and an improved coupling arrangement thereforwhereby the frequency changer system in which it is included provides asignal output of substantially uniform amplitude. i

Stated more fully, it is an object of the invention to provide animproved, mu1ti-range, tunable, oscillator system embodying an electricdischarge oscillator device and an improved frequency changer device inconnection therewith so interconnected and jointly controlled in theVarious wave bands that uniform amplitude of oscillation,

high stability and decreased reaction betweeen the elements of thefrequency changer device may be obtained together with a uniformdetector signal output at all frequency bands.

In accordance with the invention, the oscillator,

embodying an electric discharge oscillator device,

Referring to Fig. 1, a radio frequency amplifier including an electricdischarge device 5, is coupled through an adjustable coil system, ofwhich one coil or transformer l is shown, to a source of si nal energysuch as an antenna 9. The amplifier 51s in turn coupled through a coilsystem represented by a transformer II, with a first detector, frequencychanger or mixer tube l3, of the elec tric discharge type. An electricdischarge oscillator device is indicated at iii and forms part of anoscillator system, hereinafter described, for supplying oscillations tothe mixer tube i3. I latter is coupled to output leads i7. through iiintermediate frequency coupling transfer-n -i The coil system for-thehighfrequency amplifier 5 and first detector 59 may be of any suitabletype, controllable by suitable tap switches ii i, it, it and 21,connected for single control or gang operation by suitable means asindicated by the dotted connection 3! with a control knob 29. Theswitches 23 and 21 represent means for shifting the grid connections ofthe tubes 5 and it while the switches 2i and 25 represent similar meansfor shifting the antenna and the plate connec tions for tube 5simultaneously with the switches 23 and 2.1, to'the differing sets ofcoils in circuit with the tubes 6 and i3, to provide amultirangr-ituning system for the radio frequency amplifier; and firstdetector. The system is, however, adapted to provide a wide frequencyrange of operation. In'the present example the switches are arranged tocover five differing wave bands which are arbitrarily designated as theX, A, B,

bands only being shown to illustrate the particular connections providedin the present preferred system. In the circuit diagram, the coils areshifted in conjunction with suitable variable tuning capacitors 33 and35 for the radio frequency or high frequency amplifier and the firstdetector or mixer tube respectively and these are in turn interconnectedfor gang operation by suitable means as indicated by the dottedconnection 31.

For a further understanding of the wide frequency range covered by thesystem shown, the

} medium frequency range quency, medium frequency and high frequencyranges.

In the present example, in the high frequency or'D range, the first tubeor radio frequency amplifier isremoved fromthe circuit, and signals fromthe antenna are directed from the contact B of the switch 2| through alead 39 to the circuit wiring associated with the contact.D of the gridswitch 21 for the detector mixer tube f3. The wiring comprises aconnection lead 1 between the ground 43 and a tap 45, a secondconnection lead 47 between the tap 45 and thecontact D of the switch 21and a third circuit lead or wire 49 from the switch arm 21 through to apoint of connection 5| with the tuning capacitor 35 for the grid orinput circuit of the first detector 13.

In the D band or high frequency range, the inductance'of the wiringalone is utilized inconjunction with the tuning capacitor to provide anauto transformer for coupling the antenna directly to the grid of thefirst detector l3, the primary of the auto transformer comprising thewire 4| and the secondary comprising the wire 4| and the wires 41 and 49which, in the physical arrangement of a receiver, are connection leadsof sufficient size to be rigid and cut to the proper length to providethe desired inductance to tune through the indicated range with thecommon tuning capacitor 35, in the high frequency hand.

For the C band, which is within the medium frequency range, the coils ortransformer I and II are utilized to couple the antenna with the radiofrequency amplifier 5, and the latter'with the detector l3 through theswitching contacts C -of the switches 2|, 23, and 21, the inductance ofthe transformers being such that the same tuning capacitors 33 and maybe utilized to tune through the C range as above indicated. Theremaining bands B, A and X are similarly arranged and for the-purpose ofsimplifying the drawings the inductances therefor have been eliminatedsince such switching connections, are

I grid 5| is connected through an input lead 53 with the switch 23, thenthrough the coil system to a common lead 55 in which is provided afilter Cand D bands, the connections for the c and n comprising a seriesresistor 51 and bypass capacitor 59. Through the filter, the lead 55 isconnected with a lead 6| providing a suitable source of automatic volumecontrol potential as indicated. The connections for the various bandsfor the lead 55 are indicated in connection therewith.

The radio frequency amplifier 5 is provided with a self -bias resistor33 to establish an initial bias 'in addition to the automaticvolumecontrol potentials received through the lead 6|.

The first detector or mixer tube I3 is of the multiple grid type, termeda pentagrid-mixeramplifier and may be of the type 'now to be knowncommercially as RCA-6L7. This is a new commercial type of tube having agrounded metal envelope 65. It is provided with an equipotential cathode61, a control grid 69 and an output anode H. In addition, it is providedwith a suppressor grid 13 connected with the cathode, and threeadditional grids 15,11 and l8,'the latter two being screens on eitherside of the grid 15 and interconnected, whereby the latter grid isshielded from the control grid 69 'and the output anode H by the grid|'|'|8 as well as by the suppressor grid 13.

The grids ill and 18 provide a screen structure which maybe termed ascreen grid or screen for anode 1|, signals applied thereto are mixed toprovide a desired intermediate frequency signal from the output anode Hand thence through the intermediate frequency amplifier transformer l8.

The cathode 61 of the detector is provided with a self-bias resistor 19and the inductances for the D andC bands are connected to ground, the

ground for the C band being indicated at BI and for the'D band at 43,whereby the signal control grid 69 is self-biased for the said bands.For the remaining X, A and B bands,-additional automatic volume controlbias is obtained from the supply lead 6| through a filter comprising aseries resistor 81 and bypass capacitor 89. The bias supply is takenthrough taps 85 as shown for the X band which is shown complete with thecoil 83. With this arrangement, the first detector is provided withautomatic volume control in certain of the lower medium frequency andlow frequency ranges. It has been found that this arrangement tends toprovide a more uniform output from the detector as is desirable, andprevents varying load conditions from affecting the oscillator on thehigher frequency bands.

It will be noted that the radio frequency amplifier 5 is provided withan additional series resistor 9| in the cathode lead 93 and that this iscontrolled by a tap switch 95 having contacts corresponding to thecontacts of the switches previously described. The contacts B, C and Dare connected to ground as indicated at 91, while the contacts X and Aare open circuited, thereby providing means for short-circuitlng theadditional resistor 9| in the B, C and D bands only. It will be seenthat in the X and A bands the negative bias on the radiofrequencytamplifier is thereby increased by the amount of the potentialdrop in the resistor 9|. The sensitivity of the receiver for the A and Xbands is, therefore, simultaneously decreased with wave band change. Theoperating connection for the switch 95 is indicated by the dotted lineconnection 99.

In connection with the radio frequency amplifier stage it should benoted that the contact D for the grid control switch 23is connectedthrough a lead IOI with the bias supply lead 55 whereby the tube isunder control of the bias supply system although not in directoperationfor the transmission of signals. Likewise, the D contact for the anodeswitch 25 is connected with the contact C whereby plate potential ismaintained on the tube for the D band. Anode supply for the tube 5 isprovided through the supply lead I03 and in turn is connected, through afilter resistor I35 provided with a bypass capacitor II", to a potentialsupply lead I33.

In connection with the detector tube I3, the

cathode is connected to ground for radio frequency potentials throughsuitable bypass capacitors III and H3 and the screen grid 11 is likewisegrounded at radio frequencies through a bypass capacitor II5. Both thescreen grid and anode leads are provided with suitable series re- Theradio frequency amplifier tubemay be of the type known commercially asthe RCA 6K7, triple-grid control amplifier. The oscillator I5 is alsopreferably of the metal enclosed type comprising a grounded metalenvelope I29, an equipotential cathode I3I, a control grid I33, a screengrid I35, and suppressor grid I31. 'The main, anode is indicated at I39.This may be of the type known commercially as RCA-6J7. The oscillator isof the grid leak and capacitor type, the control grid I33 beingconnected through a grid capacitor I4I- to the variable tuning capacitorI43 to the contact arm of a grid switch M5 andis also connected toground I41 through a grid leak I49 and thus through the coil to thecathode. I

The cathode of the oscillator is directly coupled or connected to thesecond or outer control grid I5, of the detector I3, through aconnection lead I5I and a grid or coupling capacitor I53. a grid leakconnection I55 is provided between the grid I5 and the cathode 81. Boththe oscillator grid. I33 and the oscillation grid I5 are, therefore,grid leak and capacitor coupled to their respective sources of signalpotential. The oscillation grid I5 receives oscillations from thecathode of the oscillator.

heretofore been possible: Furthermore, because of the location of thegrids and relatively high degree ofscreening in the mixer tube I3, thereaction between the signal and oscillator circuits has been reduced,that is, the reaction between circuits connected with the grids 69 andI5. This is a material advantage in aligning the various circuitsconnected with the oscillator and detector.

Because of the electronic coupling of the secondcontrol grid I5 which isconnected with the oscillator I5, as hereinafter described, and becausethe grid I5 is well shielded, the direct coupling to the oscillatorcircuit and the capacity coupling [therewith is relatively low. Thisresults in less change of amplitude or frequency because of changes inload caused by tuning the circuit connected to the grid 69.' r

The radio frequency amplifier 5 may be of any suitable type, but ispreferably of a type comprising a metal grounded shield "9 containing anequipotential cathode I2I, an output anode I23 in association with thecontrol grid, together with a suppressor grid I25. and a screen gridI21. It will be noted that like the screen grid and anode of thedetector I3, the screen grid I2! is provided with a seriesresistor I23and the anode I23 is provided with the series resistonllli.

In connection with the automatic volume control lead 6|, the sameautomatic volume control potential is applied to all tubes and thecontrol of gain is regulated by the operation of the anode and screengrid series resistors, which, in operation, tend to raise the electrodepotentials as the control grids are caused to become more negative inresponse to increased signal strength. By properly relating theresistance in the screen and anode circuits, the gain maybe controlledwithout resorting to a-voltage divider resistor for the automatic volumecontrolcircuit. This obviates the necessity for applying differingautomatic volume control potentials to the various controlled tubes As aminer tube or first detector, it has been found thatthe electrodearrangement best adapted for a high frequency range of operation in abroad frequency. range, is with the inner grid asthe signal control gridwhile the second or outer control grid is utilized as the oscillationgrid. As fhereinbefore described, it is provided preferably with a gridleak and capacitor type of bias supply. The inner or control grid isprovided with an automatic volume controlled or a fixed negative bias.

It has been found that this grid connection prevents degenerative actionin the mixer tube as encountered heretofore in muitigrid devices whenthe outer grid is utilized as the signal grid.

With the present arrangement, having the outer grid connected to thesource of oscillations and to the cathode through a grid leak resistor,while the inner grid is utilized for the signal, the degenerative effectis not present and. the device provides signal amplification instead. Inthis connection, therefore, the inner control grid will be referred toas the signal grid and the outer control grid-as the oscillation oroscillator grid.

The control grid I33 of the oscillator is colt" 1 nected with thevarious wave band circuits conand simplifies the automatic volumecontrol 5375- I tern.

trollable by the switch I45 and a second switch I51 is provided tochange the cathode connections with said circuits. "The latter switchmay be termed the cathode coil-selector switch while the switch I45 isthe grid coil selcctor switch.

The grid coil-selector switch arm is CCIl'il'li ted with the tuningcapacitor M3 through a 1 connection or lead indicated at Mill. flYhe iiion is provided with contacts corresponding in ltllJllil ber to thenumber of wave bands to be covered, in this case five bands, and theswitclizl contacts corresponding thereto are indicated it. Wt, C and Dfor the wave or frequency h ids hare inbefore indicated, andreprcsentirl a morality of bands covering a wide frequen en tending intoa relatively high fre liency range.

The contact D of the grid col selector switcizl is connected to groundicated at it'd in or lead cont tin llfltiillil'ififti the contact D ofthe cathode selector switch I51 whereby, when the switch I51 is in theposition shown, the cathode of the oscillator is connected to the tapI61.

The combined length of the lead wires I59 and I63 is such that, withthe-switch I45 in the position shown, suflicient inductance is includedtherein to form a grid inductance for the oscillator while the lead I65to ground forms the anode inductance ofa Hartley type oscillator, thetotal inductance being tuned by the capacitor I48.

The oscillator I5 utilizes'both the main anode I39 and the screen gridI35 as anode electrodes, with the suppressor grid I31, between the twoanode electrodes, connected to ground as indicated at "I.

The oscillator suppressor grid may be tied to the screen grid of thedetector, bypassed to ground, and both grids may then be series fed fromthe positive +B supply source. This is of advantage when automaticvolume control is applied to the detector as the screen voltageregulation is then such that the voltage change of through the commonseries resistor II1.

In order to decouple the two electrodes, a filter is provided in thelead I68, comprising a series resistor I12 and bypass capacitor I14.

It has been found that variations in screen grid current causingvariation in the drop in the resistor II1, provide potential changes inthe proper direction on the suppressor grid of the oscillator tomaintain its plate or anode impedance at the proper values to counteractthe load change of the detector tending to change the oscillator outputamplitude and frequency.

The anode circuit for the screen grid I35 is completed to the ground I6Ithrough a by-pass capacitor I13 and a ground connection I15 from theanode screen grid lead I11. A series resistor I19 is provided in thelead I11 between the screen grid and the source of anode or screen gridpotential represented by the supply lead I8I. This resistor has adesirable regulating function on the oscillator which will hereinafterbe described.

The main anode I39 is connected through an output anode lead I33 to afeed back coil or winding I85, thence through a lead I01 to a secondfeed back coil I89 and is connected to a source of anode potentialprovided by the supply lead I09, through a series regulating and filterresistor I9I provided with a bypass capacitor I93. The function of theresistor I9I in regulating the osciliator and in-conjunction with theresistor I19 will hereinafter be described.

With this arrangement, the'screen grid I35 as an anode, is coupled inthe oscillator circuit through the inductance of the lead I65, with thecathode connected to the tap I61, and grid connected to the end terminalof the inductance represented by the lead I59 and the lead I63 in plingis provided through the main anode I39 and the feed back winding I85which comprises a few turns coiled adjacent to the'grid switch I45 -ininductive coupling relation to the wires I63 v and I65. An anode circuitswitch having a three element movable contact arm I95 is provided withcontacts corresponding to the selected wave bands X, A, B, C and D and,in addition, two spaced contacts I91 and I99, the latter contacts andthe contact B being engaged by the three element contact and connectedto ground 20I, in

the position shown. In this position, through the contact I91, the mainanode circuit is shunted to ground through a bypass capacitor 203 on thelow potential side of the feedback winding I85. The alternating currentpath from the main anode to cathode therefore, includes not only thefeed back winding I85 but also the lead I65 or anode inductance, throughthe ground connections 20I and I6I.

The contact C of the switch I95 is connected through a bypass capacitor205 to the lead I83 and thereby to the anode I39 for connecting theanode directly to ground through the switch arm when the switch arm ismoved to the left as viewed in the drawings to engage the contact C,

and because of the triple arm, the contact C is connected to ground forthe positions B and A of the switch I95. Since the contacts B, A and Xare blank in the position X, the ground 20I is each connected throughseries capacitors 221, 229

and HI, respectively, to corresponding contacts C, B and A on the gridcoil selector switch I45 through suitable grid leads 233, 235 and 231.

The inductance for the X band as indicated at 239 is an inductancewithout tap having the grid end connected to the contact X of the switchI45 to a lead 24I and having the opposite end connected. to ground 243through a series adjustable capacitor 245. Each of the inductances forthe X, A, B and C bands is provided with shunt terminal capacitorsindicated at 241 and the series capacitor 23I for the grid circuit ofthe A band is also provided with a shunt trimmer capacitor indicatedat249.

With this arrangement it' will be seen that the cathode I3I of theoscillator and the oscillation grid 15 of the first detector or mixertube may be connected to differing tap points on the various inductanceelements for the various wave bands to be covered, while the controlgrid connection may be made to the grid ends of the inmain anode seriesthrough the switch 145. Additional cou- 7'5 ductances for the bands C, Band A through series capacitors 221, 229 and 23I, respectively. The gridconnection for the band X is made directly to the inductance 239. Theinductance of the lead I59 between the switch I45 and the tuningcapacitor I43 for the oscillator has a negligible effect in the lowerfrequency bands, such inductance having less than one percent of theinductance in the B band coils.

For the C, B and A bands, the oscillator anode connections for both thescreen grid I35 and the I39 are completed through the grounded ends ofthe inductances and the bypass capacitor 205, directly from the anodelead I33 and through the bypass capacitor I13 from the screen grid leadI11, both anode electrodes being thereby effectively coupled through theinductances of the C, B and A band.

band A is connectedthrough a lead I" with the Q contact X are'blank.;The main movable contact 1 said inductances are ineffective tointer!the operation of the D'band inductance It will be noted that to; the xreceives oscillator Also. it will be seen that for theC -Bfand A 2 bandstheseriescapacitors 221, 22! and!!! are for the X band is included inthe alternating cur- 5 rent path from the anode I. In thiscase thescreen grid I35 is ineffective to set up voscillations.

It will be noted that the lead 225 from the intermediate tap iii of theinductance III for the.

contact D of the anode short-circuiting switch Iii. This is for thepurpose of short-circuiting to ground the anode portion of theinductance 2H for the bands C and D aswell as tl' 1e'- band* .8 sincethis is the largest of the solenoid in-'-, ductances and it has beenfound that thesarne tends to break up into portions which resonate atcertain of the higher frequencies; tuned through on the C and D bandsunless thesame j is soshort-circuited. i The grid ends of theinductances-for-the B, and (Hands are also short-circuiti-tofmund'thereby to render the .inductances ineffective to resonate atfrequencies in the; next adjacent, lower bands, by a grid Ishort-circuiting Iii having contacts D, C, B, A, x and two additionalcontacts Ill adjacent to the contact]! in sequence-of operation. whichcontactsr withthe 25! comprises three fingers for engagingthreeadjacent. contacts simultaneously in a similar manner to the switch I..The contact D of the switchm it connected t the .{lead m throughalead-QI" and similarly the contacts C and B;are. connected throughleads if with the; leads 235 and 231., respectively rangementfbeing suchthat in. the

for 3 the D band, the" inductances for} g c. n and'A are V efbands shortcircuited to groundthr'ough a lead 2" and .a groundconnection illgfwheeby 40 try.

by the rigid wiring i5! and lif -ill .As th switch "I is moved in aclockwies directionfas viewed in" the drawings, the short-circuit isprogressively removed from the C, B and-Akband inductances until thecontact reachesthe'posltion! with the extreme left hand contact. arm asviewed in the drawings, at the contact'X,-;when

all short-circuiting of the inductances is removed forthe x bandoperation.

- The grid and cathode coil selector switch its and in together with theanode andglld coil short-circuiting switches it! and iii arsprefer ablyinterconnected for simultaneous operation in the relation shown and asindieated by the dotted connections fill.

anqoperationthe cathode switch lllis connected@tl rougli the contact X,thence-through theentird coilifofthe band A to ground, whereby theinductahce'ioffthe coil is included in the cathode circui which coil aportion of the oscillator v, appear and will-thus be transferred flation grid IS. I In all of the other cillatlon grid 1! is connected acportion of the oscillatorcoil or ind V voltage therefrom directlyr,

included in circuit with the tuning capacitor n and in the highpotential side of the circuit. This arrangement forthe A', B and 0 bandshas the effect of changing the grid excitation over the This useof agedeveloped is least at the low frequency ends of the bands but the gridis effectively shifted toward the cathode at the low frequency and byvirtue of the'ratio between series. and tuning capacitors so thattalarger percentage of. the oscillator voltage appears from cathode toground;- l0

On the highest frequency range D, a low frequency winding I8! isprovided in the plate circult of the pentode oscillator 15 to obtainoscillation over the low frequency end of the D band.

It will be noted that this winding is provided with a shunt tuningcapacitor 261. This is for the purpose of tuning the winding l8! belowthe tuning'range of the D band, but adjacent thereto. The winding andshunt capacitor'fl'l constitute a tuned circuit in the main anodecircuit which isresonant to a frequency preferably below the lowestfrequency to which the oscillator is tunable in the D band. Therefore,atany'frequency within the tuning range of the D band this circuit willact capacitively and the value of the capacitive reactance will increasewith decrease infrequency. The arrangement is such that the circuit is,therefore, eflective only in the lower. frequency portion ofthe D bandof theoscillators. This circuit is also used to regulate the rate ofchangeof frequency as the oscillator is tuned over the D band, show upthl'soscil vlator at the low frequency end, so that the oacillator willtrack with the antenna circuit without the necessity of including aseries capacitor. In

order that the oscillator circuits may inore readily be understood thesimplified circuits representative of the. low frequency, mediumfrequency and high frequency connections have been redrawn without theswitching, bypass and other elements, in Figs. ,2, 3 and 4, Fig. 2, jshowing the general circuit arrangement for the medium frequency or A, Band. Chanda, Fig. 3 showing the circuit arrangement for the highfrequency or D band,

and Fig.4 showing the circuit arrangement 'for.

the low frequency or 3 band. The same refer ence numerals have beenusedthroughout in referring to the corresponding circuits and elementsthereofas in Fig. l.-

Referring to ;2, it will be seen that the screen grid "I and the mainanode ifl'of the oscillator i are each bypassed to ground through bypasscapacitors 2.5 and I'll, respectively. here by being connected throughthe ground lit-to the anode end of the inductance 2 across which isconnectedthe tunlngcapacitor I. The cat ode I is connected to theintermediate tap Ill .and to the lead -l5l-for the'ili'stdetectoroscillation grid. The controlTgrld III is coupled through its grid leakand capacitor lit-4M, to the grid and of the inductance 2i 1, therebyprovidinga Hartlfil' y e oscillator. The suppressor; grid I31 providesan effective screen between the twoanode electrodes "I and ISL g H Y apentode device as an oscillator has been found to beeifective inproviding im- I provedoscillator stability and uniform oscillatoroutput. Additional means for stabilizing the output comprises-the seriesresistors 'lll'and" iii between the supply meana'indicated at 2"; and)the-anode electrodes. The power supply means 1",; represents anysuitable power supply for the receiving system, operated from a variablesource of power such as alternating current and arranged to supplyheating current to the apparatus.

The two series resistors in the anode circuits prevent the internalimpedance of the oscillator tube and, therefore, the frequency of theoscillator system from varying appreciably from a predeterminedadjustment. The voltage on the two electrodes is maintainedsubstantially constant since the tendency to increase the B supplyvoltage tends to provide an increasing current and an increased drop inpotential. This is further made more effective by the fact that theheater current is derived from the same source and simultaneously withan increase in B potential, the heater current is correspondinglyincreased, thereby causing an increased plate current and an increaseddrop in potential through the resistors I19 and I'9-I.

By way of example, if the B voltage is 200 volts and assuming theresistors I9I and H9 to be so chosen as to provide a 40 volt drop, theanode potentials will thus be 160 volts. If the B voltage were toincrease 10% to 220 volts, the plate and screen current would beincreased approximately 10% causing a 10% rise in voltage across theresistors to a total of 44 volts and r the new anode and screenpotential would then be 176 volts.

However, because of the increased filament voltage of 10%, there will.be an increase in 29% or to a value of 53 volts. Subtracting 53.

volts from the 220 volts B supply will provide a potential of 167 voltsat the two anodes which is only slightly more than a 4% increase 7, overthat with normal B supply voltage although the supply voltage hasincreased 10%.

The effect of the combination oflvthese teatures is to cause the plateresistance of the oscillator tube to remain substantially constantregardless of the voltage impressed thereon and, therefore, theoscillatory system tends to maintain the same frequency throughout verywidely varying conditions of supply voltage.

It will be seen ,that both anodes, that is, the screen grid and the mainanode are provided with a return circuit to cathode through the anodeportion of the inductance 2| I thereby providing an oscillator of theHartley type having two anode electrodes separated by a grounded screenelectrode and with the cathode and output connection floating aboveground.

It will be noted that the A band inductance is selected for illustrationin Fig. 2 as representing the other circuits of the medium frequencybands. In this connection the series capacitor 23I between theinductance and the tuning capacitor is shown. As has been pointed outhereinbefore, this is also a compensating c'apacitor for causing theoutput of the oscillator to be more uniform, thereby to apply to thefirst detector substantially the same output voltage for the highfrequency and low frequency ends of the band. It will further be notedin Fig, 2 that the bypass capacitor for the anode I39 is the capacitor205, this connection being provided by the switch I95 in the A, B andbands as will be seen by referring to Fig. 1 thereby eliminating bothfeed back windings I85 and I89 from the alternating current circuit.

Referring now to Fig. 3, the connections for the high frequency or Dband are shown in connection with the oscillator I5, the inductance ofthe rigid bus wiring being shown in conventional manner as inductancesat I and at I58- I63. It will be seen from an inspection of Fig. 3, thatthe change in connections effected therein includes removing the seriescompensating condenser 23I (Fig. 2) from the high side of the tunedcircuit and adding the tuned feed back winding I which is tuned adjacentto and below the frequency band covered by the oscillator circuit inorder to maintain the strength of the oscillations constant over theentire tuning range of the oscillator. This is done by boosting the lowfrequency end of the range by added feed back provided by the coil I85.It will also be noted that the bypass capacitor 203 is now effective inthe main anode circuit caused by operation of the switch I therebybypassing the feed back winding I89 shown in Fig. 1. The compensatingresistors I9I and I19 are effective in the anode electrode circuits tomaintain the plate impedance of the oscillator substantially constant asdescribed in connection with Fig. 2.

Additional stability is obtained at the high frequency end of the D bandby so proportioning the value of grid, anode and tuning capacltors andof the grid and anode inductances that the oscillator is effectivelystabilized as to variations in voltages and load. The grid and anodecapacitors may be made of equal value, and the grid and plateinductances I63 and I55 are of equal value without magnetic couplingbetween this provides an additional stabilizing feature which is used toadvantage over the higher frequency portions of the D range.

. The first detector receives energy from the oscillator across theinductance I65 or the anode portion of the oscillator inductance as inthe medium frequency range of the circuit shown in Fig. 2. This methodof coupling the oscillator cathode with the second control grid of themixer tube provides a relatively low load on the oscillator.

As in the preceding figure, and in the Ine-' dium frequency ranges, bothoscillator anode electrodes I35 and I39 include the anode inductanceportion I65, the connections between the anode electrodes and thecathode comprising the capacitors 203 and H3 to ground, the ground IBIof the main tuning inductance, thence through the inductance element I65t0 the oathode I3I from the tap I6'I on the main tuning inductance. Bothanode electrodes are thereby effective to maintain oscillations whichare reinforced in the low frequency end of the tuning range of theoscillator by the feed back winding I85.

It will be noted that the anode electrodes I35 and I39 are shielded bythe suppressor grid I31 which is connected to ground as in the mediumfrequency range.

Referring now to Fig. 4, the connections for the low frequency or X bandrange of operation are 51102711.

In this circuit the first detector is supplied with oscillations fromthe inductance 2I I of the A band introduced into the cathode circuitbetween the cathode 3I and ground '2 I3 and is shunted merely by thetrimmer capacitor'241. Accordingly, it is tuned to a relativelyhighfrequency above the tuning range of the oscillator for this band andoperates .as an inductance to. provide coupling with the first detectorthroughthe lead II.

The oscillation are set up wholly by feed back from the coil I89 and themain inductance 239 is not tapped but is utilized entirely in the gridcircult of the oscillator. Since the oscillator is required to cover. arelatively narrow frequency range (1.42) the output may be maintainedconstant without special means other than provided by the coilintroduced in the cathode circuit.

It will be noted that the inductance of the feed back winding I85 ofFig. 1 has been omitted since its inductance is negligible in this rangeand the bypass capacitor for the main anode I39 is indicated at I93.

The suppressor grid I31 is utilized as a screen between the anodeelectrodes I35 and I39 as in the other frequency bands and thecompensating resistors HI and I19 operate in the same manner tostabilize the oscillator frequency with variations in supply potential.

In the low frequency range it will be seen that K the oscillator systemis changed from the Hartley circuit to the feed back circuit with thescreen grid I35 effective to control the internal impedance of theoscillator and the main anode I39 utilized for setting up oscillationsby feed back.

The oscillator inductance is a single winding without taps. The feedback-arrangement shown with its absence of taps is therefore decidedlyadvantageous in eliminating absorption circuits which would fall in ahigher frequency band.

Furthermore, the inductance in the cathode lead which is coupling meansfor the detector, provides an impedance from which to take the detectorload without tapping into the tuned circuit. The inductor 2 being in thecathode lead is in a circuit common to the grid, screen and plate.

Therefore, while the screen grid is not provided with a return circuitthrough the main tuning inductance it is nevertheless coupled with thecontrol grid and with the main anode through the inductor 2| I.

Referring again to Fig. 1 along with Figs. 2 to 4 inclusive, it has beenpointed out that the oscillator circuit is arranged to cover arelatively wide frequency range of operation in a series of separatebands, while providing improved frequency stability and uniformity ofoutput over the various tuning ranges. The oscillator operates onfundamental frequencies which are supplied to the first detector on anauxiliary mixing grid which in this case is the second control grid. Theoscillator generates signals which, in all bands, are above thefrequency of the incoming signal by the amount of intermediate frequencywhich,

in this case, is chosen at 460 kilocycles.

As shown in the drawings, the cathode of the oscillator is above groundpotential for high freformer or coil being provided by the circuitwiring. Four selector switches are provided, the switch I95 being theanode coil short-circuiting switch, the switch I being the coilshort-circuiting switch and the switches I45 and I51 being the grid coiland cathode coil selector switches respectively. The witch I45 serves toconnect the grid of the oscillator and the main tuning capacitor I43 tothe proper coil for the range to which the switch is adjusted. Theswitch I51 serves to connect the cathode and the first detector to theappropriate part of the circuit being the plate or anode portion of theinductance for all bands except the X band when it introduces aninductance in the cathode circuit for coupling with the detector.

The switch I95 serves to bypass the inductance I85 which is the D bandfeed back coil when the A, B or Cl ranges are used. However, as thiscoil has such .low inductance it is not necessary to bypass it when thelong wave length band X is in use. The switch I95 also serves to groundquency oscillations while the anode or plate is effectively at groundpotential. This arrangement together with the plateand screen seriesresistor causes the circuit to be substantially independent of powersupply variations in regard to stability and uniformity of output.

Separate coils or transformers are used for each of the tuning ranges.The switching of the different bands is such as to short-circuit certainunused coils which would absorb energy from the circuit in use.

The overall oscillator circuit comprises five separate transformers orcoils, the D band transbands B, C or D are being used. The switch 25Iserve to detune the coils of the three bands immediately below theone-being used. This detuning is accomplished by connecting the seriescondensers for the A, B and C bands across the coil, thus tuning it to alow frequency and avoiding any possibility of interference with thehigher frequency bands in use by the absorption of v energy.

In the case of the A band coil, since it is divided into a large andsmall section by the tap there is a tendency for the lower or platesection of the coil to resonate in band C and D although the whole coilis detuned. Therefore, the plate portion is short-circuited also inaddition as above described, through the switch I95.

The coil for the 1) band comprises merely a piece of rigid wireextending from the ground to the switch l5 and thence, when theswitch isthrown to the position D, through to the tuning capacitor I43. Thecapacitor tune the piece of It is,

rigid wiring to the proper frequencies. therefore, necessary that thelength of the wire and. the location of the same be maintained inposition after adjustment.

Because of the extremely high frequency to which the oscillator respondsit is necessary that exceedingly short ground connections be used atcertain points. For example, as shown in Fig. 1, the heaters and thecathodes are preferably bypassed directly to ground at the tubeterminals except at the'oscillator, the cathode 'of which is used forcoupling purposes. In this connection it 'direct ground connection asindicated at 28I ad- 'jacent to the tube terminals.

Likewise the shield or metal envelope of the oscillator is directlyconnected to ground, a rninimum length of lead being used. Th se directconnections are of importance in order to prevent spurious osc llationsor responses at the h h frequency end of D band, as the circuits withinthe detector tube, i. e. the elements thereof have na ural periodscorresponding to frequencies of 480-220 megacycles. The harmonics of theoscillator that fall in the range of 180-220 megacycles so excite thedetector tube that responsesdenoted by hiss output at intermediatefrequency are obtained. In order to prevent these spurious responses, itis necessary to have the filaments,

minimum of impedance at 200 megacycles. In some cases it may bedesirable to include a trap in the oscillator coupling lead tuned in theneighborhood of 200 megacycles to prevent the oscillator harmonics fromreaching the detector. Such a circuit is shown at I52, and may consistof a 9 micro-microfarad capacitor I54 connected across several inches ofthe lead ll providing an inductor I56 between the oscillator cathode andthe detector coupling condenser I53.

This trap may also be inserted at I58 in the detector cathode lead toprovide degeneration at 200 megacycles.

From the foregoing description it will be seen that an oscillator, firstdetector or frequency 'changer system is provided wherein Ta) Minimumreaction is. obtained between the oscillator andthe radio frequency orsignal input circuits and minimum loading of the oscillator.

the D band alone.

(e) The oscillator output voltage delivered to the first detector ormixer tube is uniform throughout the various wave bands covered therebyimproving the emclency of conversion in the flrst detector or mixertube. The automatic volume control is simplified, sincethe screen gridand anode circuits are controlled by suitable series compensatingresistors regulating the gain of the system in response to strongsignals of high amplitude.

While the combination has been shown and described in connection with a5'band superheterodyne receiving system, it should be understood that itmay be applied to similar systems having fewer or a greater number ofwave bands for wide frequency range coverage.

I claim as my invention: 1. In combination, an electron discharge deviceincluding an input electrode, an output electrode and a pair ofadditional electrodes, a resonant circuit connected to said inputelectrode and tunable over a range of frequencies, and feedback meansfor supplying energy to said resonant circuit, said means including apair of paths coupled respectively between said output electrode andsaid circuit and between said pair of additional electrodes and saidcircuit, said feedback paths being connected in aiding phase relationand having reactive constants so proportioned that saidpaths areindividually effective primarily over different complementary portionsof saldfrequency range and provide a preselected and substantiallyuniform feedback of energy throughout said'frequency range.

2. The invention as set forth in claim 1 wherein one of said additionalelectrodes is a screen shields and cathodes of the first detector andoscillator tubes grounded by paths which have a this includes a range of17.8 to 73 megacycles for grid interposed between said input electrodeand said output electrode and is effectively grounded for high frequencycurrents.

3. The invention as set forth in claim 1 wherein said additionalelectrodes are interposed be-' tween said input and output electrodesand are eflectlvely grounded for high frequency currents.

4. In combination, an electron discharge device including an inputelectrode, an output eleconant circuit, said means including apair ofpaths coupled respectively between said output electrode and saidcircuit and between said additional electrode and said circuit, saidfeedback paths having reactive constants so proportioned that said pathsare individually effective primari- 1y over different complementaryportions of said frequency range and provide a substantially uniformstrength of oscillations throughout said frequency range. 5. Incombination, an electron discharge de vice including an input electrode,an output electrode, a cathode and an additional electrode effectivelygrounded .for high frequency currents, a resonant circuit connected atits high potential end to said input electrode and tunable over a rangeof frequencies, a connection from an intermediate point on said circuitto said cathode, and feedback means for supplying energy to saidresonant circuit, said means including a pair of paths coupledrespectively between said output electrode and said circuit and betweensaid additional electrode and the low potential'end of said circuit,said feedback paths having reactive constantsso propertioned that saidpaths are individually effective primarily over din'erent complementaryportions of said frequency range.

6. The invention as set forth in claim 5 where- I .in said outputelectrode path is primarily effec tive in' the lower end of said range.

7. In combination, an electron discharge de vice including an inputelectrode, a output electrode and an additional electrode, a resonantcircuit connected to said input electrode and tunable over a range offrequencies, and feedback means for supplying energy to said resonantcircuit, said means including a pair of paths coupled respectivelybetween said output electrode .and said circuit and between saidadditional electrode and said circuit, said feedback paths havingreactive constants s0 proportioned that said paths are individuallyeflective primarily over difierent complementary portions of said fre-'quency range. v

8. The invention as set forth in claim 7 wherein the feedback path fromsaid output electrode resonates adjacent the low frequency end of saidrange. I

9. The invention as set forth in claim 7 where in said additionalelectrode is a screen grid disposed between sald input and outputelectrodes.

10. The invention as set forth in claim 'I ftrodea pair of additionalelectrodes, a resonant circuit including an inductor element connectedat its high potential end to said input electrode and tunable by avariable capacitor element over a range of frequencies, and feedbackmeans for supplying energy to said resonant circuit, said meansincluding a pair of paths connected respectively between said outputelectrode and said circuit and between one of said additional electrodesand said circuit, the other of said addi tional electrodes beingeffectively grounded for high frequency currents, said feedback pathshaving reactive constants so proportioned that said paths arindividually effective primarily over different complementary portionsof said frequency range, said output electrode feedback path includingan inductor and capacitor in parallel resonant relation below saidfrequency range and coupled inductively to said resonant circuit.

12. The invention as set forth in claim 11.

wherein said cathodeis connected to an intermediate point on saidinductor element,'the low potential end of said inductor element beingeffectively grounded for highfrequency currents.

13. The invention as set forth in claim ll wherein said inductor elementconsists. of two substantially equal inductance portions, the

i said second circuit being coupled to said first cirtween said outputelectrode and said additional electrode in shielding relation therewith,and regulating means connected to said output electrode and additionalelectrode.

18. The invention as set forth in claim 7 wherein the feedback path fromsaid output electrode resonates adjacent the low frequency end of saidrange and regulates the rate of change in frequency of said tunablecircuit, by slowing up the rate toward the low frequency end of saidrange.

19. In an oscillator for a superheterodyne receiving system, an electricdischarge device including a cathode, an input and a plurality of outputelectrodes, a first circuit tunable over a band of high frequenciesconnected to said input electrode, to said cathode, and to one of said0114 put electrodes for feeding back energy to cause' said circuit tooscillate, a second circuit tuned to resonate adiacent the low end ofsaid band,

cult to regulate the rate of change in frequency of said tunable circuitby slowing up the rate cathode being connected betweensaid portions,

- and regulating means are connected to said output electrode and one ofsaid additional elecl4.*The invention fas setiforth in claim 11 1wherein said [inductor element consists of two substantially equal, anduncoupled inductance portions, said cathode .saidportions. a

being connected between l5. Theinvention asset forth in claim 11wherein, 'saidinductor element consists of two substantially; equal anduncoupled inductance portions, said cathode'being connected betweengportionsfand individualregulating resistors I r connected between apositive potential supply frailty of output electrodes, a first circuitcontoward the low frequency end.

20. The invention as set forth .in claim 19 wherein said second circuitis connected to one of said output electrodes and to said cathode forfeeding back oscillatory energy'to said first circuit.

21. In an oscillator for asuperheterodyne receiving system, an electricdischarge device including an input electrode, a cathode and a plunectedto said input electrode and to said cathode and tunable over a band offrequencies, a

connection from one of said'output electrodes to said circuit forfeeding back energy to cause said circuit to oscillate, a second circuitfixedly tuned adjacent and below the low frequency end of said tuningrange connected to another of said output electrodes and to said cathodewhereby said second circuit reacts capacitively, the capacity reactanceincreasing with decrease in frequencyv of'said tunable circuit, saidsecond circuit being coupled to said first circuit and characterized bya regulating effect upon the rate of change of frequency as the tunablecircuit is tuned toward the low frequency end of said range. I

JOHN D. REID.

